In the course of daily lives, people encounter many different objects. Objects routinely must be kept track of so that they can be found after a period of non-use. Some objects are used frequently and routinely so that a user can generally recall where the object is located in accordance with the routine. For example, a user may charge her phone on a night stand each night, so that the phone can be expected to be on the night stand the next morning. Similarly, a user may leave his car keys in a tray near the garage when he returns home from work each day, so that the keys are easily located in the same spot the following morning. Sometimes, however, routine is broken and an object is left at an unusual location or lent to another person for a period of time. Other objects are used infrequently but must be readily accessible when needed (and some are even intentionally hidden), such as a hidden spare house key, a birth certificate, or a vehicle title.